1. Field of the Invention
The present invention relates to an expandable rubber-modified styrene resin composition to obtain a molded foam having an excellent impact resistance and pliability as well as a high expansion ratio and also relates to a molded foam obtained by said expandable rubber-modified styrene resin composition.
2. Description of the Related Art
A molded foam made from a polystyrene resin is employed widely as a container and a heat insulating material for its excellent shock-absorbing properties and heat-insulating properties as well as easiness in molding into an article. However, because of its insufficient impact resistance and pliability which may cause formation of cracks and breaks, it involves problems such as difficulty in applying to a package for a precision instrument.
On the other hand, a molded foam made from a polypropylene resin requires a large-scaled device for molding although it has excellent impact resistance and pliability. Further, its resin characteristics also requires a transportation from a manufacturer to a molding company in a form of pre-expanded beads. As a result, a production cost becomes disadvantageously high.
Recently, a rubber-modified styrene resin molded foam which is easy to be molded and has improved impact resistance and pliability compared with a polystyrene foam has been proposed in Japanese Laid-Open Patent Publication Nos.3-182529, 5-116227, 7-11043 and 7-90105.
Nevertheless, the impact resistance and the pliability of a conventional molded foam is improved only to a limited and insufficient degree, and attempts to achieve a high expansion ratio result in obtaining a molded foam having a poor appearance due to shrinkage and a reduced strength. Accordingly, it is impossible to use a molded foam as being foamed at a high expansion ratio, resulting in a limitation in package resource saving.